The present invention refers to a compressor system with a water-injection cooled compressor in a cooling water circuit.
Such compressor assemblies are employed to compress gaseous media, especially air, and to provide this as a pressure gas. Water is used for sealing, lubricating and cooling the compressor, which has the advantage over oil not to be detrimental to health or the environment. DE 44 47 097 describes a water-cooled compressor system in which the compressor is formed as a screw-type compressor. The cooling water is injected in the area of the rotors of the compressor and reseparated from the compressed gas after leaving the compressor. The water heated in the compressor is then guided towards a cooling means. Then the cooled cooling water is filtered and re-supplied to the compressor. In this process, various parameters of the cooling water can be changed by evaporation of the cooling water or by absorption of humidity from the air into the cooling water: if the relative salinity of the water increases because of evaporation of cooling water, an increased amount of deposit precipitates, which might cause damages and defects in the narrow sealing gaps and to the sealing rings. Deposit formation is kept low by a polarization means, which does not, however, prevent the salinity from rising. If, on the other hand, the salinity of the cooling water decreases because of humidity absorbed from the air, the buffer ability of the cooling water to absorb free carbon dioxide is reduced. Yet free carbon dioxide in the cooling water which is not buffered (bound) is very aggressive and corrosive. The Ph-value of the cooling water might also be changed by evaporation of cooling water, absorption of humidity from the air into the cooling water or absorption of copper or iron ions, so that the cooling water has a corrosive effect.
From DE 821 993 and US 722 524, compressors are known that use distilled water for cooling. Distilled water is rather expensive and is very delicate with a view to its pH value.